The reliability of power distribution systems is dependent on many variables such as load capacity, customer base, maintenance, and age and type of equipment. However, the variable that is most often responsible for degraded reliability is weather, and common weather conditions are often overlooked in reliability analysis. These conditions include, but are not limited to, rain, wind, temperature, lightning, humidity, barometric pressure, snow, and ice.
Common weather does not include catastrophic events, such as hurricanes or tornadoes, which exceed reasonable design or operational limits of the electric power system. There are existing methods that define major reliability events, including catastrophic weather events and that exclude the resulting interruptions from the calculation of reliability indices.
Much of the focus of modeling the effects of weather on power distribution systems has remained on extreme weather conditions. There are also existing methods that include weather as a factor in the analysis of specific fault causes. However, methods that use the combined effects of common weather conditions to predict the total number of daily or by shift interruptions are not presently available.
There is a need for methods that can predict daily or by shift power distribution system interruptions based on common weather conditions, and for interruption risk assessment based on immediate weather conditions. A related method of normalizing reliability indices for common weather conditions is also needed to improve reliability assessments of power distribution systems.